youths aged between 13 to 24 are at the centre are infected with HIV 15 million youths worldwide have HIV and some youths dont even know they have HIV, some people have no signs of HIV until later stages antibodies are testing to see if a person is HIV postive

I was told that only after 7 weeks of having sex with an HIV positive person the virus can be detected in a healthy [HIV negative] person. During this 7 weeks period the HIV multiply and grows. My question is, during this period, can a strong immune system can fight off the HIV and defeat it, kill it? For example, if I'll eat only healthy food, exercise, etc' - and have a strong immune system, I can prevent myself from having AIDS? Even though I had unprotected sex?